There is no doubt whatsoever that the operators were not at fault. The cause of the failure was due primarily to "several" serious design flaws that could allow the reactor to almost instantly become catastrophically and explosively super-critical with the extraction of A SINGLE control rod past its maximum specified limits.
Considering the maintenance history and records of "sticky" control rods its very likely that during maintenance the operators accidentily jarred loose a rod trying to free it. The design of the reactor was such that within 14mS of this the reactor instantly pulsed up to 20GigaW and they were dead or dying. No chance ever to recover and correct from a simple error.
All reactors of this type were then modified to inherently restrict control rods from being pulled past the design limit so this could never happen again.
These poor buggers died because serious design flaw wasnt remedied or controlled. A lesson to us all.